1. Field of the Invention
This invention relates generally to a semiconductor laser drive circuit in a laser beam printer. More particularly, it relates to a semiconductor laser drive circuit which can stably output a laser beam and has a considerably simplified construction.
2. Background Art
Recently, a so-called "laser beam printer" has been extensively used in which an electrostatic latent image is formed on a photo-sensitive material by scanning the photo-sensitive material with the laser beam. The laser beam is modulated according to the image data of figures, characters or the like, and the latent image thus formed is subjected to a copying operation including a developing step, a transferring step and a fixing step to obtain a hard copy of the image data. Especially popular has been a small inexpensive laser beam printer using a semiconductor laser.
On the other hand, there has arisen a strong demand for a semiconductor laser drive circuit for a laser beam printer using a semiconductor laser, such as a laser diode, which can compensate for changes of the output (the laser beam) of the semiconductor laser due to its temperature variation and its aging. Such compensation prevents the semiconductor laser from damage, for instance, due to overcurrent, and eliminates erroneous modulation. However, to be practical, such a drive circuit must have a low manufacturing cost. Unfortunately, semiconductor laser drive circuits which can fully satisfy these differing requirements have scarcely been proposed in the art.